How does a single speaker play many simultaneous frequencies?

05 June 2011

Question

I've been an avid listener for only the past month or so when I've been listening to the podcasts on my walk to and from the library everyday to revise, and am absolutely loving it so far and have managed to get through a good 30 or 40 of the latest podcasts in this short period of time... Anyway just a few things I was wondering if you could help me with:

As an amateur musician and DJ I have forever struggled to work out how it is that, particular in cheaper more basic speakers, a single speaker cone/diaphragm is able to vibrate at so many different frequencies at any one time in order to produce the full tonal frequencies of a piece of music? So essentially: how is it that it is able to recreate a kick drum at say 70Hz whilst still producing a clear strings note of 1700Hz undisturbed. Thanks very much for your time

Dom Parker

Answer

Dave - If the speaker was to produce a single frequency, think what that actually means - it means that the speaker is moving backwards and forwards, and causing the air to move backwards and forwards in a sin wave pattern. You've probably seen a sin wave. It's basically just a very specific zigzaggy wiggly line. Now, if the speaker moves in any other pattern than that, you could imagine it's moving slowly with a big wiggle and then on top of that superimposed, there's a little wiggle. So, moving in and out slowly but on top of that is kind of vibrating a little bit. So then it would be outputting sound with the low frequency, the big slow wiggle, and also a much higher frequency as well, at the same time. The way that sound works is you can superimpose the motion of the speaker, you can superimpose lots and lots of different vibrations and that will produce sounds of lots and lots of different frequencies, all at the same time by just making the right pattern for the speaker to move back and forwards. It's not moving in a smooth wiggle, it's doing something incredibly complicated and that's a mixture of lots of different frequencies.

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